SYNTHESIS, CHARACTERIZATION, AND THERMODYNAMIC ANALYSIS OF A 1+1 SELF-ASSEMBLING STRUCTURE BASED ON THE CYANURIC ACID.MELAMINE LATTICE

This article describes the reaction of the trivalent melamine derivative C6H3-1,3,5-[CO2(CH2)4OCOC6H4-2-NH-C3N3(NH2)(NHCH2CH2C(CH3)3)]3 (homoflexM3, h-flexM3) with the trivalent isocyanurate derivative C6H3-1,3,5-[CONHC6H4-3-N((CH2)17CH3)COC6H3-2-NC(O)NHC(O)NHC(O)-5-O(CH2)17CH3]3 (hubCA3) in CHCl3 to afford a structurally well-defined 1 + 1 supramolecular aggregate h-flexM3.hubCA3. This structure is held together by a network of 18 hydrogen bonds and is one of the most stable nonbiological supramolecular aggregates synthesized to date. The structure was characterized by H-1 NMR and UV spectroscopies, gel permeation chromatography, and vapor pressure osmometry. The exchange reaction between h-flexM3.hubCA3 and C6H3-1,3,5-[CO2(CH2)4OCOC6H3-2-NHC3N3(NH2)(NHCH2CH2C(C-H3)3)-5-CH3]3 (h-flexM'3, a close structural analog of h-flexM3) was monitored by H-1 NMR spectroscopy. This exchange reaction appeared to occur by dissociation; the reaction was first-order in h-flexM3.hubCA3 and zero-order in h-flexM'3. The transition-state parameters, DELTAH(double dagger) = 24 +/- 2 kcal/mol, DELTAS(double dagger) = -6 +/- 12 eu, and DELTAG(double dagger) = 26 +/- 6 kcal/mol, for the exchange reaction were calculated by following the exchange process at several temperatures. These thermodynamic data indicated that the average enthalpy per hydrogen bond in this system was 1.3 +/- 0.1 kcal/mol. Several mechanisms by which the exchange reaction may occur have been postulated and discussed.